Unidirectional Emission of High-Q Modes in Deformed Microcavity Lasers

Abstract

We propose two types of deformed microcavity lasers, where a high-$Q$ mode group emits unidirectionally. First, the emission characteristics of an oval-shaped microcavity laser are studied. In experiments, modes localized on periodic orbits emit unidirectionally with a narrow in-plane divergence angle of about 12 degrees. The origin of high directionality is elucidated by means of classical ray dynamics. Wave calculations show that the $Q$-factors of the resonances are higher than $10^8$. We explain this extraordinary high-$Q$ factor in relation with a dynamical barrier region where Kolmogorov-Arnold-Moser curves significantly obstruct leakages of resonances. Second, the rounded D-shape cavity is comprised of three circular arcs and one linear section. To minimize diffraction effects from the boundary, three circular arcs and one linear section are tangentially connected. By adjusting the sizes and the positions of the two sub-circular arcs, unidirectionality is maximized. In an experiment with an InP based InGaAsP semiconductor microcavity laser, a lasing mode group localized on a period-7 unstable periodic orbit emits unidirectionally. In our resonance calculation, High $Q$-factors of this group of modes localized on a period-7 unstable periodic orbit are confirmed. Last, the characteristics of the modes localized on marginally unstable period orbit are studied experimentally. We selectively excite modes localized on three different MUPOs and modes localized on three different. In experiment, we experimentally show that MUPO modes are more robust than the modes localized on unstable periodic orbits against surface roughness. When we compare the characteristics of MUPO resonances with the resonances localized on stable periodic orbits in wave calculations, the emission intensities of MUPO resonances are stronger than those of stable resonances while the $Q$-factor of the MUPO resonances are similar to that of the stable ones.